1. Field of the Invention
The present invention relates to a line-fed phase-controlled antenna comprising a plurality of individual radiators disposed in a symmetrical surface for generating a sum pattern and a difference pattern which is generated by anti-phase amplitude excitation of the individual radiators at both sides of the line of symmetry, whereby a transition zone is also provided along the line of symmetry between the antiphase amplitude excitations.
2. Description of the Prior Art
As with standard radar antennae which are equipped with a primary radiator system and a parabolic reflector, electronically phase-controlled antennae can be operated in a so-called mono-pulse method for increasing the accuracy of target locating and of tracking wherein a sum pattern and, usually, two difference patterns for the azimuth plane and the elevation plane are employed. In order to enable a flat structure and in order to optimize the amplitude illumination and, therefore, the side lobe attenuation in the sum diagram, line feed is frequently employed in phase-controlled antennas, whereby each of the individual radiators is driven via a line belonging to a distributor network. Therewith, however, the optimum amplitude illumination over the antenna surface for the sum pattern is also effective with respect to magnitude for the azimuthal and elevation difference patterns, for which it is no longer optimum, but generates relatively high side lobes which only decrease slowly extending from the axial antenna direction.
A far-reaching optimization of the sum and difference amplitude illumination can be achieved in the case of utilization of the radiation feed principle by way of special measures at the quadruple primary radiator. What is disadvantageous, due to the radiation feed, is the great structural depth of the phase-controlled antenna arrangement and the limited accuracy for achieving a rated illumination as required, for example, for a maximum side lobe level of -40 dB.
The article by H. Oettl and L. Thomanek entitled "Monopuls-Antenne der Bodenstation fur Satellitenfunk der Deutschen Versuchsanstalt fur Luft-und Raumfahrt e.V." in the periodical "NTZ", 1968, No. 10, pp. 631-634 discloses a line-fed phase-controlled antenna comprising a plurality of individual radiators disposed in a symmetrical surface for generating a sum pattern and two difference patterns which are generated by antiphase amplitude excitation of the individual radiators at both sides of two lines of symmetry. The two lines of symmetry divide the antenna surface into four quadrants. A meshing of the antiphase amplitude excitation is also provided along these lines of symmetry when generating the difference patterns. The meshing derives in that two lines of symmetry are equipped with individual radiators between the quadrants and belong to the neighboring quadrants in alternating sequence. This phase meshing for the formation of the difference pattern contributes to an improvement of the side lobe behavior and to the suppression of diagram shoulders in the difference pattern. However, optimized sum pattern, azimuthal difference pattern and elevation difference pattern cannot be formed with this phase meshing applied in a monopulse antenna, particularly in phase-controlled antenna arrangements comprising many individual radiators.
An application of three separate distributor systems for optimized sum channel, difference azimuth channel and difference elevation channel require three inputs per individual radiator having great impedance, cross-connection and loss problems.